Moreover, it is known that a hydraulic installation may include a plurality of hydraulic machines all fed in parallel by a pipe on the upstream side. Accordingly, during maintenance operations on a valve, it is necessary to work on the valve dry, i.e. without fluid inside it. This has the disadvantage that the arrival of fluid on the upstream side of the valve, in the pipe, must be shut off and therefore feeding of the other hydraulic machines of the installation must be stopped. This drawback is moreover exactly the same for valves installed on other fluid distribution networks. This is economically disadvantageous because the production or the distribution of fluid is stopped during maintenance operations on the valve. The smooth bearing, disposed around the journal, is subjected to friction forces by the journal that are generated by the force of the water on the obturator and by the weights. It is therefore necessary to repair it or to replace it several times over the service life of the hydraulic installation. The same problem arises for valves used in other fluid distribution networks.
EP-A-0 834 032 describes a valve designed so that, during maintenance operations, it is possible to access some components supporting the journal such as the smooth bearing. The above document describes a valve in which it is possible to replace the bearing parts without evacuating all of the water on the upstream side. To this end, the valve described uses upstream and downstream sealing rings, these rings providing the seal between the obturator and the body of the valve. These sealing rings are movable axially in the direction of flow of the fluid inside the valve by pressurizing the space between the body of the valve and the blocking member, which pushes the sealing rings into contact both with the blocking member and with the body of the valve. This technology is applicable only if the blocking member is a ball, i.e. only for a valve of spherical type. Moreover, in the method described in this document, in order to remove the parts supporting the journal and the journal itself, it is obligatory to demount the downstream sealing ring in order to install a cover on the downstream side of the valve, as this makes it possible to balance the pressure of the fluid on the upstream and downstream sides of the valve and therefore to prevent the journal or the parts supporting the journal being subjected to the thrust force on the obturator caused by the pressure of the fluid. The problem with this device is that if the upstream sealing ring is not tight enough, i.e. if the pressurization of this ring is not sufficient, fluid invades the interior of the body and maintenance operations are impossible. Moreover, dismantling the parts supporting the journal and/or the journal necessitates decompression of the space between the body of the valve and the obturator, which can lead to the upstream sealing ring moving and causing a leak. Moreover, this valve does not include any mechanical device enabling the journal to be kept perfectly centered in the bore. This can lead to the journal being off-center and therefore a fortiori the obturator being off-center and can therefore cause leaks placing personnel in danger during the maintenance operation.
It is these drawbacks that the invention is more particularly intended to remedy by proposing a system integrated into the valve whereby maintenance operations on the bearing are facilitated, more reliable, and applicable to any type of obturator.